In recent years, a power supply device mounted on a vehicle is required in order to provide the vehicle having a motor driving a hybrid car or an electric car. In such a vehicle, the power supply device has a comparatively high output for driving the motor. The power supply device having the high output is configured by connecting a lot of secondary battery cells in series. Since the secondary battery cells generate heat by charging and discharging, according to an increase of the number of the secondary battery cells, the amount of heat generation is increased. In the power supply device having a lot of the secondary battery cells, a heat radiation structure is necessary where the heat radiation of the secondary battery cells is efficiently heat-conducted and emitted.
In response to such a request, a power supply device having a heat radiation structure has been developed (for example, refer to Patent Literature 1). As shown in FIG. 15, this power supply device includes:                cooling plate 103 which incorporates heat exchanger 104 configured to forcibly cool by the heat of evaporation of a coolant circulating inside;        assembled batteries 102 which each connect a plurality of battery cells 101, and are fixed on this cooling plate 103; and        frame structure body 105 which fixes cooling plate 103.        
Thus, the power supply device forcibly cools assembled batteries by cooling plate 103.